In a mammal, the humerus is the long bone of the upper portion of each anterior limb, for example, the human arm. As is commonly known in the art, the end of the humerus closest to the mammal's vertebral column is termed the proximal end and the end furthest from the mammal's vertebral column is termed the distal end. Further, the terms proximal and distal can be used to describe the relative orientation along the long axis of the humerus of any two points. For example, the anatomical neck of the native human humerus is proximal relative to the surgical neck of the native human humerus.
In Homo sapiens, the humeral head at the proximal end of the native humerus articulates with the glenoid cavity of the scapula to form the shoulder joint, and the extremity at the distal end articulates with the radius and ulna of the forearm to form the elbow.
A number of cancers can arise in the proximal portion of the humerus. Such cancers can include, but are not limited to, osteosarcoma, enchondroma, Ewing's sarcoma, periosteal chondroma, osteochondroma, chondroblastoma, chondromyxoid fibroma, aneurismal bone cyst, simple bone cyst, giant cell tumor of bone, chondrosarcoma, fibrous histiocytoma, fibrosarcoma of bone, and plasmacytoma, among others. Also, secondary tumors can form in the proximal portion of the humerus as a result of metastasis of primary tumors in other parts of the body. For example, about 15-20% of breast cancer patients develop humeral metastasis. Alternatively or in addition to chemotherapy or radiation, and if the tumor is not so advanced as to call for complete amputation of the limb, surgical resection of the tumorous region of the humerus can be performed as part of treatment. Surgical resection of the tumor frequently further involves resection of nearby soft tissues, such as the rotator cuff, the deltoid muscle, or at least one tendons or ligaments.
There are four main limb reconstruction options available after surgical resection of the proximal humerus: osteoarticular allograft reconstruction, allograft prosthetic composite, endoprosthetic replacement, and arthrodesis (the surgical fixation of a joint to promote bone fusion). The main goal of these reconstruction procedures is to stabilize the remainder of the upper extremity so the hand can be used in space. However, these procedures generally have poor functional results around the shoulder. These results are in most cases due to large amounts of soft tissues and soft tissue connection sites removed with the tumor to obtain a safe margin. The soft tissue resections can include the whole or part of the rotator cuff, the deltoid muscle, or other soft tissue structures and attachment points surrounding the proximal humerus. These resections limit the stability of the joint and the functional results.
Segmental endoprosthetics and allograft prosthetic composites are the most frequently used treatment options. Osteoarticular allografts are rarely used because of the risk of fracture of the humeral head. Arthrodesis is generally performed only if a resection removes a portion of the scapula containing the glenoid cavity.
All current treatment options are able to reconstruct the resected bone but in most cases there is an additional even larger need to address the soft tissues that stabilize the shoulder and provide active function. In most cases there is considerable loss or resection of soft tissue and soft tissue connection sites around the proximal humerus. Also, bone grafts in osteoarticular allografts or allograft prosthetic composites frequently suffer from resorption of bone. Therefore, a need exists for proximal humerus prostheses capable of imparting superior joint stability and functionality than those known in the art.